1. Field of the Invention
This invention relates to a driving force distribution mechanism for a vehicle which distributes a driving force from a driving source to left and right driving wheels.
2. Description of the Related Art
Japanese Patent No. 2641724, for example, describes a conventional driving force distribution mechanism for a vehicle, which distributes and transmits driving force of a driving source, such as an engine changed in speed through a transmission, to left and right driving wheels (left and right wheels). Specifically, this patent literature discloses a driving force distribution mechanism that has a mechanical differential device, left and right clutches capable of transmitting torque to left and right wheels respectively, and left and right transmission mechanisms (speed-up mechanisms).
This driving force distribution mechanism described in Japanese Patent No. 2641724 is designed such that the left and right wheels are driven by the mechanical differential device in a state in which the left and right clutches are disengaged. Also, one of the driving wheels can be rotated faster than the other driving wheel by bringing one of the left and right clutches into engagement and the other in disengagement.
However, the driving force distribution mechanism described in Japanese Patent No. 2641724 is configured such that the left and right clutches and the change gears of the left and right transmission mechanisms are disposed on a single intermediate shaft provided parallel to an output shaft. Use of both the right side and the left side of the intermediate shaft as describe above brings out the problem of an increase in size of the driving force distribution mechanism and size of a housing accommodating the driving force distribution mechanism, which leads to an increase in weight thereof and a deterioration in mountability.
Moreover, as a technology for performing left-right wheel torque difference control by using a differential mechanism of an existing final reduction device, driving force distribution mechanisms described in, for example, Japanese Patent No. 3103779, International Publication WO2006/114331 and the like. However, because a plurality of planetary gear mechanisms are used as speed-up mechanisms in the driving force distribution mechanism described in Japanese Patent No. 3103779, the problems of this driving force distribution mechanism are that an extremely large number of parts are required and it is extremely difficult to produce this driving force distribution mechanism, which leads to a significant increase in the production cost. In the driving force distribution mechanism described in International Publication WO2006/114331, on the other hand, internal gears in complicated shapes are used as the speed-up gears; which brings out the problems of a complicated structure for supporting these gears and a significant increase in the production cost.